bnx2x: Fix GSO for 57710/57711 chips

Starting with commit 91226790
`bnx2x: use FW 7.8.17', the bnx2x driver no longer requests the FW to perform
IP checksums for IPv4 packets.

This behaviour needs to be revised for 57710/57711 chips -
when using GSO, if the driver will not set the IP checksum flag then packets
will be transmitted by the chip without a valid IP checksum, resulting in
a drop of all such packets on the receiver-side.

Signed-off-by: Yuval Mintz <yuvalmin@broadcom.com>
Signed-off-by: Dmitry Kravkov <dmitry@broadcom.com>
Signed-off-by: Eilon Greenstein <eilong@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>